Add notification for context saved

Source/DATAStack.swift

@@ -400,6 +400,7 @@ import CoreData
         } else {
             let contextBlock: @convention(block) () -> Void = {
                 self.mainContext.mergeChanges(fromContextDidSave: notification)
+                NotificationCenter.default.post(name: .NSManagedObjectContextMergedChanges, object: context)
             }
             let blockObject: AnyObject = unsafeBitCast(contextBlock, to: AnyObject.self)
             self.mainContext.perform(DATAStack.performSelectorForBackgroundContext(), with: blockObject)
@@ -415,6 +416,12 @@ import CoreData
     }
 }
 
+public extension Notification.Name {
+    static var NSManagedObjectContextMergedChanges: Notification.Name {
+        return .init("NSManagedObjectContextMergedChanges")
+    }
+}
+
 extension NSPersistentStoreCoordinator {
     func addPersistentStore(storeType: DATAStackStoreType, bundle: Bundle, modelName: String, storeName: String?, containerURL: URL, isExcludedFromBackup: Bool) throws {
         let filePath = (storeName ?? modelName) + ".sqlite"